Catalyst materials used within oil refinery reactor vessels are routinely changed and the catalyst material is either discarded (if it is significantly damaged) or cleaned and re-used. Conventionally the catalyst is unloaded from the reactor vessel under vacuum. Catalyst is expensive and therefore damage to the catalyst has a significant impact on costs. Analogous problems occur with the conveying of other particulate materials, such as fragile or breakable particulate materials.
The existing vacuum systems which are used to draw particulate material such as catalyst from inside a contained location such as a containment vessel such as (for example a reactor) and through to access holes to a receiving vessel such as a cyclone, hopper or the like cause a considerable amount of damage to the particulate material, with up to 60% of the material being scrapped in the case, for example, of a catalyst material.
One of the causative factors of this damage within the existing systems is that the velocity of the particulate material is uncontrolled in the conveying path (usually a duct or hose) which extends from the pick-up point in the first vessel (e.g. the reactor) to the receiving (second) vessel (e.g. a hopper or cyclone). Furthermore the velocity of the particulate material on entry into the receiving vessel is very high due to the very high expansion rate of the conveying gas as it changes from atmospheric pressure at the pick-up point in the first vessel, to approximately ⅓ of a bar absolute in the receiving vessel (e.g. hopper or cyclone). This has the effect of increasing conveying velocity from approximately 15 m/sec (which represents an exemplary minimum pickup velocity) or more to approximately 45 m/sec at the receiving vessel. This latter velocity tends to cause severe breakage of particulate material such as catalyst in the terminal part(s) of the duct or hose near the receiving vessel and on the internal walls of the receiving vessel itself.
The present invention therefore seeks to provide a device, system or apparatus which reduces the damage caused to fragile particulate material, such as catalyst, as it is conveyed under negative pressure from a first vessel (such as a reactor) to a receiving vessel such as a hopper or cyclone.
The present invention further or alternatively seeks to enable the use of substantially similar equipment, devices or apparatus, with any necessary minor alterations or changes of configuration, both to unload under negative pressure particulate material such as spent catalyst from a first vessel such as a reactor and also to load particulate material such as catalyst with compressed air into a first vessel such as a reactor under positive pressure. This latter loading process of leading under positive pressure is described in our co-pending International patent application No. PCT/GB2006/002363.